Influence of the protein source on rat adiposity during energy restriction.

The aim of this study was to assess modifications of body composition after a high protein, energy‐restrained diet in overweight rats, with emphasis on the effect of the protein source. 56 rats received an obesity induction diet (OI) for 5 weeks. A control group (n=8) remained on the same diet whereas other rats were restricted (‐40% of energy intake) for 3 weeks with either the same diet (n=8) or with a 33 % protein diet (HP) formulated with casein, whey, soy or mixes of casein:whey (50:50 or 80:20). Control OI rats exhibited a higher adiposity than restricted rats (+29%, P<0.0001). Whatever the diet composition, the energy restriction elicited the same body weight loss characterized by a decrease of fat mass without lean mass change. Compared to control OI rats, the epididymal adipocyte sizes were lower in rats consuming the OI restricted diet (‐10%, P<0.05), the soy and the casein:whey 80:20 diet (‐20%, P<0.05). Compared to OI‐restricted rats, the effect of restriction was greater in the casein:whey 80:20 group (P<0.01). Our results reveal that, under energy restriction, the nature of the protein does not impact weight loss and body composition within a short period but are likely to generate changes on a longer period. Gene expression measurements in adipose tissue are in progress.